New DNR study looks at composition of hooks and fish survival

OUTDOORS

The Department of Natural Resources has advocated for some time that releasing undersized or inadvertently caught fish might best be done by cutting the line and leaving the hook imbedded.

The reasoning has been that immediate removal of hooks from gill, gullet or stomach would overly stress or unduly injure the fish. By simply cutting the line, it was expected that the hook would rust away or be rejected over a period of time.

During late summer and early fall of last year, the Fisheries Division of DNR reintiated a study to determine the effects of different types of hooks imbedded in rockfish.

The results of that study may be especially helpful in the selection of hooks for the spring trophy season for rockfish, during which time it is likely that many smaller fish will be hooked in pursuit of that one legal fish over 36 inches.

The latest DNR study is a follow-up on a similar study in 1989, which was determined to be faulty because of unequal test conditions. The purpose of the study was to look at the impact on short-term and long-term survival of the fish and to investigate the effects of hooks with different finishes -- bronze lacquer, nickel plating, tin-cadmium plating and unfinished steel.

In a nutshell, the study suggests that rapid rust rates do not occur and that the composition or finish of the hook may adversely effect the survivability of the fish.

However, according to a report on the study which recently was released by DNR, current practices and hook styles apparently will not cause slow and debilitating diseases.

In the study, the DNR used wild striped bass taken from Kent Narrows and the Bay Bridge on hook and line to ensure all were hooked through the snout. Fish were separated by size (under 56 centimeters and over 57 centimeters) and transported within six hours to the Cooperative Oxford Biological Laboratory, where the smaller fish were placed in open water pens and the larger fish were put in a 4,000-gallon tank.

Both small and large fish were held for four weeks, during which they were expected to acclimate to test conditions and test diets.

Water flow for the tests was taken directly from the Tred Avon River. Physical parameters of the test were pH steady at 7.2, dissolved oxygen from 6.0 to 8.0 parts per million of water, salinity from 9.0 to 15.0 parts per thousand of water, and temperatures ranged from 1.50 to 2.3 degrees Celsius.

The research project was separated into the following categories: hook-coating studies; hook-rust studies, and barbed hooks vs. barbless hooks.

No. 2/0 hooks were implanted to simulate natural strikes on a fisherman's line.

In the hook-coating studies, rejection rates were determined for 30, 60, 90 and 120 days after implantation. Bronze was the most readily rejected, followed by steel, tin-cadmium and nickel.

None, however, exhibited a significant differential in rejection. The nickel-coated hooks, did show a tendency to break.

In the rust-rate study, 31 of 33 fish rejected their hooks completely within 20 days after being hooked in the stomach. Because of the rate of rejection, rust rate based on coating style could not be determined. However, it does suggest that stomach hooking does not pose a significant threat to the fish.

In terms of barbed vs. barbless hooks, the barbless hooks were rejected at a higher rate. However, the study said, there is no significant rate difference between the two.

Mortality in the hook-coating study was a cause of concern, according to the report. Six of 30 fish hooked with tin-cadmium-plated hooks died, opposed to one each for bronze and nickel and none for stainless.

No mortalities were recorded during the rust-rate study.

In the barbed-barbless tests, barbed hooks appeared to produce a significantly higher rate of mortality.

The report does not explain why the tin-cadmium hooks produced unusual mortality, but it does theorize that since cadmium has been shown to have pronounced effects on immune response and on cellular survival, this might be the cause.

The barbed-hook mortality also could not be easily explained and might be attributable to husbandry of the test stocks rather than the hooks.